Think back. Have you ever thought that a person you knew well was acting strangely? Giving you the creeps. Yes, especially your significant other. Was he, she, it behaving very unlike themselves? And you thought that, if it were possible, that person could be someone else altogether? Remember that feeling. It’s akin to a bizarre occurrence you could experience on some future star trek. It’s an indication that some event or entity has either altered someone or replaced them altogether. They literally have become someone else.

“Rubbish!” you say. But it happens too frequently to ignore. Even trainers are checked out from time to time to make sure we are who we think we are. (Something you may also want to consider.)

You haven’t already forgotten the infamous Dr. Janice Lester who molested Captain James T. Kirk by switching bodies with him? By instituting a “life energy transfer” alien technology, she left the real Captain Kirk feminine, weak and helpless. Of course, if she’d had a kick-ass female body from planet Amazon, she wouldn’t have needed the transfer in the first place.

Hopefully, you’ll commit this one to the collective memory. This same Captain Kirk beamed up to the Enterprise from a planet that got really cold at night (no, it wasn’t Vulcan). He seemed fine, except for a little dizziness, but Chief Engineer Montgomery Scott held his hand anyway and led him out of the transporter room, leaving it empty. Because of this chief’s sycophantic behavior, another Kirk materialized on the transporter pad, looking like a wild man. Much like the “real” Kirk after consuming a flask of Saurian brandy.

I only love you for your Saurian Brandy.

After roughing up Dr. McCoy and stealing his Saurian Brandy, The Impostor, as he came to be known, found Yeoman Janice Rand’s quarters where he tried to have his way with her. When Rand promptly reported him, the “good” Kirk insisted, “It wasn’t me. It wasn’t me!” But Crewman Fisher, who the “evil” Kirk also attacked (but wasn’t as frisky with) corroborated her story. Only Mr. Spock had his back, stating what any sentient crew member would think. “There’s only one logical answer. We have an impostor aboard.”

But The Impostor, upon hearing this in Kirk’s quarters, yelled, “I’m the captain. I’m Captain Kirk!” And proceeded to disguise scratches he’d received from Rand with makeup found on Kirk’s dresser. (Not going to touch that.) He then went to the bridge to prove this fact, where “good” Kirk and Dr. McCoy finally found him, cornering the evil twin, who then gave up since he wasn’t having any fun.

Parasitic-controlled, white-haired old men trying to take over the Federation.

But evil duplicates aren’t the only beings you have to beware of. In this example a hundred years later, upon being summoned to a clandestine meeting consisting of three starship captains, Captain Jean-Luc Picard was told wild stories of a conspiracy involving the highest officials in Starfleet Command and, of course, his response was, “Rubbish.”

But his good friend, Captain Walker Keel, insisted, saying, “Some of us have seen strange patterns emerging. Unusual orders. High ranking officials backing irrational proposals. Dammit, Jean-Luc, I tell you some of Starfleet’s top command are changing. Some of my friends, I’ve known for years, are bluffing their way through talk of old times.” To which Picard responded, “Poppycock!”

But after his good friend’s ship, the Horatio, was destroyed, Picard thought a trip back to Earth may be in order. Especially, since Data found further evidence of shenanigans. When they arrived, the hostility Starfleet Admirals demonstrated by offering him a bowl of worms as a pre-dinner appetizer pretty much convinced him. So, he and Commander William Riker duked it out with the parasitic-controlled, white-haired old men trying to take over the Federation. Apparently, symbiotic crabs had taken over their bodies and controlled their brain functions. Though, the mother parasite, in the end, felt deeply misunderstood and only wanted the promise of a “peaceful co-existence,” a steady stream of phaser fire ended her hopes of ever achieving it.

Poor thing. At the beck and call of any idiot that invokes his name.

And last, but certainly not the least, the Emergency Medical Holographic program (EMH) or, The Doctor, as he was affectionately called, had altered his program for the worse by downloading behavioral subroutines from holodeck recreations of famous historical figures. Apparently, “a dark thread” in the personalities of these famous folks congealed and added what can only be described as a “Mr. Hyde” personality to The Doctor’s “Jekyll.”

After discovering the Doctor’s hand upon her knee, Lieutenant B’Elanna Torres had an epiphany, saying, “Doctor, there’s something wrong with your program.” But Mr. Hyde put The Doctor to sleep and after overpowering Torres, demanded that she help him delete Doctor Jekyll. Why? Because The Doctor was, “Servile, pathetic, at the beck and call of any idiot that invokes his name. The thought of him sickens me.”

Needless to say, Mr. Hyde’s plan didn’t work. His subroutines destabilized, erasing him from The Doctor’s holographic matrix when he beamed back aboard Voyager, following a futile attempt to escape.

As you can see, in all four examples, not only was there an abrupt and noticeable change present, but the change agent’s distinct hostility toward the original person or species was apparent as well. Dr. Lester body-jacked Kirk. Kirk’s impostor attacked crew members. The parasitic lifeforms served bad food. And Mr. Hyde made derisive remarks about the good Doctor.

This is one of the major signs to look for when determining if something is amiss. That, and rage, amorous behavior, incoherency, virulent narcissism, self-aggrandizement, memory problems, destabilization and an aggressive instinct for survival. Look for these indications as you travel. Make sure that you know the crew well and report even the smallest consistency-discrepancy in them. Always keep in mind that the possibility of a switch, a body double, parasitic lifeforms, or evil holographic behavioral subroutines are real. Who knows, you may, not only, save a starship captain’s life but, perhaps, your own as well and even prevent the demise of the Federation itself.